Vibration is a well-known problem associated with rotating machinery, such as turbo machinery. Synchronous vibration (SV) is caused by a rotating mass imbalance, and frequently occurs when the mass center of the rotor is not coincident with its geometric center. Another form of vibration is non-synchronous vibration (NSV), which occurs when a radial deflection of the rotor results in tangential force normal to the deflection. The magnitude of the tangential force increases with the deflection, and the system will become unstable if there is insufficient damping, resulting in undesirable vibration. Damping the vibration in a turbo machine provides quiet, comfortable, and efficient operation of the machine, reduces fatigue stresses on the machine and its supports, and safeguards against damage that can be caused by unstable vibration.
The most common approach to reducing the impact of vibration on rotating machinery components, particularly with regard to NSV, is to provide a squeeze film damper (SFD). Typically, a bearing rotatably supports a shaft in the machinery, such as a rotor shaft in the example of a jet engine. The bearing is, in turn, supported by a SFD. The SFD damps vibrations from the rotor by providing a constant flow of oil to an annular chamber surrounding the bearing. The oil film can be squeezed through one or more exit channels when the bearing moves from its central position as a result of rotor shaft eccentricity. SFDs are not ideal because they offer sub-optimal damping characteristics while still requiring oil and maintenance. Additionally, due to the oil required, SFDs are limited to regions of the rotating machinery that operate below a threshold temperature.
It would thus be desirable to provide an effective means for NSV damping that is not temperature limited. Other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying drawings and the foregoing Background.